Light emitting diodes (LED or LEDs) are solid state devices that convert electric energy to light, and generally comprise one or more active layers of semiconductor material sandwiched between oppositely doped layers. When a bias is applied across the doped layers, holes and electrons are injected into the active layer where they recombine to generate light. Light is emitted from the active layer and from all surfaces of the LED.
In LED package design, two challenges are thermal management and size. In an exemplary conventional surface mount design, an LED or LED array is mounted onto a printed circuit board, with wire bonding present for each individual LED; the circuit board is mounted to a heat sink; and the heat sink is mounted to a fixture housing, along with needed drive electronics. Additional optics or components may be needed. Spacing between each individual LED in an array is dictated by the presence of the wire bond (i.e., there is a limit to how close together the LEDs may be). There is a continuous drive to reduce the size of LED packages to facilitate more widespread use of LEDs.
It is known that thermal management is a concern with electronic packages, whether containing integrated circuits or discrete components such as diodes or power transistors. It is also known that excessive heat may cause LED failures. Thus, one of the considerations for designing LED packages is effective thermal management. One of the objectives of effective thermal management in the design of electronic packaging is to maintain the operating temperature of the LEDs and other active circuit components at an appropriately low enough temperature to prevent premature component failure. Various cooling strategies including conduction heat transfer are in common use. However, high intensity LEDs that emit light principally in the visible part of the electromagnetic spectrum can generate significant amounts of heat that is difficult to dissipate using conventional techniques.
The design considerations of reducing the size of an LED package and maintaining a relatively low operating temperature are to some extent competitive with each other. It is desirable to develop an LED package that addresses these design considerations.